In the field of semiconductor device and magnetic device, an ultra-thin film is formed to realize more sophisticated functions and higher performances of thin-layered stack materials with layer thickness is increasing. Moreover, in the modern technology devices, interfaces structure of stacked films are also controlled in order to control electron scattering at the interfaces.
In the related art, the ellipsometry method or fluorescence X-ray method are used as a method for evaluating thickness of films to be stacked. The ellipsometry method is used to detect thickness and refractive index of a thin film as a sample by inputting a polarized light to a thin film sample having a flat front surface and by measuring changes in polarized state of the reflected light. However, this method has a problem that measurement is possible only for a sample that is transparent for the light because the light is used. The fluorescence X-ray method is used to estimate thickness of a film by measuring intensity of a fluorescent X-ray generated from a sample. In the case of this method, however, only a total quantity of element having generated the fluorescent X-ray can be detected. Namely, this method has problems that this method cannot measure in direct thickness of film and thickness of film cannot be analyzed separately when plural thin films including the identical element are stacked. In addition, both ellipsometry method and fluorescence X-ray method cannot obtain the information of an interface of the stacked films.
Observation of cross-sectional TEM of a device enables measurement of thickness of films to be stacked with very higher space resolution. Moreover, it is also possible to estimate interface width. However, a sample must be divided into many thin fractional pieces in size of 10 nm or less for TEM observation, meaning a destructive analysis. Accordingly, this method can be used for analysis of a fault but cannot be applied to an inspection apparatus.
As a method for non-destructively measuring thickness and interface of films to be stacked, an X-ray reflectivity method has been proposed. This X-ray reflectivity method may be classified into a couple of kinds. In one method, an X-ray of single color is inputted to a sample nearly in contact with the front surface thereof and reflectivity is measured while an incident angle is varied. In the other method, a white x-ray is inputted to a sample and dependence on wavelength of reflectivity is measured. In these methods, film thickness is analyzed on the basis of interference of X-rays reflected from the front surface of sample and interfaces thereof. In addition, since an interface width gives influence on reflection at the front surface and interface, width of each interface of films to be stacked can also be obtained by analyzing in detail an X-ray reflectivity profile. For a theoretical curve that can be used for analysis of reflectivity, a numerical equation obtained by introducing the effect of unevenness of interface into a recurrence formula of Parratt [Phys. Rev. 95, pp359 (1954)] (Non-patent document 1) proposed by Sinha, et al. [Phys. Rev. B, 38, pp2297 (1988)] (Non-patent document 2) is used. Moreover, the method proposed by Sakurai, et al. [Jpn. J. Appl. Phys. 31, L113 (1992)] (Non-patent document 3) is often used.